Preparation of carbon black



Patented June 6, 1944 PREPARATION OF CARBON BLACK Max B. Vogel, Easton, Pa., and John W. Snyder, Scotch Plains Township, Union County, N. J., assignors to Binney and Smith Company, New

York, N. Y., a corporation of New Jersey No Drawing. Application December 5, 1941, Serial No. 421,844

18 Claims.

This invention relates to the treatment of carbon black for use as a pigment in the preparation of liquid coating compositions such as enamels, paints, inks and the like. The present application is a continuation in part of our application filed February 24, 1940, which issued as Patent No. 2,266,104, on December 16, 1941.

An important object of the invention is to provide a specially treated form of carbon black adapted to be introduced, either directly or indi- ,rectly, into liquid coating compositions of the oil or resin type containing drying compoundssuch as compounds containing the common drier metals, manganese, cobalt, and lead or naturally occurring drying' compoundsan important feature of the invention residing in the fact that the treated carbon black serves in its full capacity as a pigment without seriously retarding the drying rate or the drying stability of such coat- 1 ing compositions.

The invention also aims to provide a method of treating carbon black, and also to provide a coating composition of the oil or resin type including. such treated carbon black as an ingredient.

In the preparation of liquid coating compositions of the oil or resin type it is common knowledge that when carbon black is used as the pigmenting agent such compositions require high percentages of drying compounds, and that in many cases, even with this increase in drying compounds, 9. longer time is required for drying than when most other pigments are employed. This is believed to be largely due to the highly active nature of the carbon black particles and also to the afllnity of the carbon black contained in the coating composition for the drier metals.

Thus, when carbon black is introduced into the coating composition, portions of the drier metals are attracted by the carbon black particles and are rendered ineffective. Attempts have been made to compensate for this phenomenon by increasing the drier metal content. This has been partly successful as regards accelerating the drying rates of freshly made enamels. However, as such enamels age the drier metals appear to lose their eflicacy and eventually reach a stage where the enamels become unusable. 0n the other hand, if sufficient drier metals are added initially to produce a satisfactory drying effect after aging for a suitable period, there is then likely to be too much drier present to permit the use of the enamel with good results when freshly made. It is common practice to overload carbon black enamels with drier metals, and when such an enamel is sent out from the factory it is with the expectation that it will remain on the dealers shelves and age before use. This, however, involves an element of uncertainty and, furthermore, the addition of excess drying metals is objectionable for the reason that this adversely affects the film durability and other physical characteristics of the enamel.

In accordance with the present invention it is proposed to treat the carbon black prior to its introduction into the liquid coating composition so as to make possible black enamels of improved drying characteristics. This treatment involves wetting the carbon black with an aqueous solution or suspension of a compound, the character of which will be more particularly described later, and then removing excess moisture from the carbon black.

Carbon black particles are of very small diameter, ranging from millimicrons for the coarsest type to less than 25 millimicrons for the finer types. Because of this extreme fineness, a small amount of carbon black, in bulk, presents a very' large surface; for example, one pound of a fine grade of carbon black will have a surface area of more than 15 acres. Each unit of surface has highly adsorptive properties which, multiplied by'the total area of the surface, render carbon blacks very active. It is a purpose of this invention to inactivate such surface, as far as its effects upon the drying of coating compositions is concerned, this result being accomplished by means of certain inactivating compounds, hereinafter referred to as inactivators. Among such inactivators which have been found to be particularly effective are the inorganic salts of chromic acid, as will be more particularly pointed out lateron.

One example of the process by which the inventionwas carried out is as follows: Approximately 300 grams of carbon black were wetted by 700 cc of water in which were dissolved 30 grams of KzCrzOr. Following this wetting, the resulting mass was dried to a moisture content of two per cent or less leaving approximately 330 grams of treated carbon black.

respectively, by weight.

Thirty-one grams of this treated carbon black were ground 48 hours in a l-quart ball mill with 2050 grams steel balls together with the following vehicle:

Grams Glytpal #2458 (50% alkyd resin in petroleum spirits) x lnl 80 At the end of the 48 hour grind, 187 gms. of Glyptal 2457 were added and the grinding continued for one hour. An enamel was prepared from the above glyptal-carbon black paste according to the above formula:

The petroleum hydrocarbon derivative was of the type sold under the trade name of "Solvesso N0. 2." The resin solution is known in the trade as Rezyl 113-G. The drier, containing 9.7% metal, was prepared as follows:

Parts by weight Manganese naphthenate, 6%Mn grams 100 Cobalt naphthenate, 6% Co do 171 Lead naphthenate, 24% Pb do 72 This enamel, tested at intervals of two weeks over a period of sixteen weeks, showed an average drying time of 5.8 hours; whereas a similarly prepared control enamel using untreated carbon black required 15.5 hours to dry.

As another example of a mode for carrying out our method, the inactivator may be formed by reacting chromic acid with a metal compound. For example, 18 gms. of CrOa were dissolved in 700 cc. water and used as a treating solution for 300 gms. of carbon black, intimately mixed with 24 gms. basic lead carbonate. The excess water was subsequently driven ofl leaving approximately 3 30 gms. of treated carbon black. Thirtyone gms. of this treated carbon black were ground in a ball mill with the resin vehicle, and subsequently formulated into an enamel essentially in the same manner as described in the first-mentioned example given above. The drying time for this enamel over a sixteen weeks period was 6.7 hours, compared with 16.1 hours for a control enamel prepared from untreated carbon black.

In order to determine the comparative eilece tiveness of various inactivators, numerous specimen enamels were prepared according to the procedure of the examples given above, using different inactivator-s for the treatment of the carbon black. In all cases the proportion of inactivator to carbon black was 1 part to 10 parts, In addition. to such specimen enamels, a control enamel was prepared in a similar manner except that the carbon black used therein was untreated. Because atmospheric conditions exert a marked influenc upon drying time, the absolute drying times are not significant standing alone. Therefore, in order to afford a more reliable basis of comparison the drying times of the enamels prepared from the variously treated carbon blacks have been correlated against control enamels each prepared at the .same time and under similar conditions as the experimental enamels. All experimental enamels and controls weretested when freshly made and at two-week intervals thereafter for a period of sixteen weeks, the average drying time for this period then being calculated. All of the treated carbon blacks show drying times substantially shorter than that of the untreated carbon black, and, therefore, indicate improved drying characteristics.

Carbon black pigmented enamels Average drying time Inactivptor Experimental Control enamel enamel Copper dichromate 5. 5 16. l Zinc dichromate 7.0 i6. 1 Manganese chromate 7.1 16. 1 Calcium chromate... 5.3 l3. 6 Cadmium chromate 6. 6 13.6 Chromium dichromate 6. i 13.6 Cobalt dichromate. ll. 1 l3. 6 Magnesium chromate. 5. 4 13. 6 Strontium chr0mate. 5. 8 13.6 Nickel dichromate 6. 0 i3. 6 Sodium dichromate... 6. 2 l4. 2 Ammonium dichromat 5. 8 13.6 Potassium dichromate. 7.8 15. 5 Ferric dichromate.. 6. 8 l6. 1 Load chromate 6. 7 16. 1 Potassium chromate 5. 8 19. 3

While the exact reactions involved by the use of inactivators have not been definitely established, we do know that the surface of carbon black particles is highly active in adsorptive power and chemical reactivity. It is this activity which is responsible for poor drying behavior generally, and it is known that drying retardation varies directly as the degree of activity of a carbon black. Untreated, active carbon black will interfere with the normal drying of an oil or resinous film by adsorbing a large part of both the added metallic compounds and the organic driers naturally present inthe vehicle. Such carbon black will also affect the vehicle and driers chemically in such a way as to produce drying retardation. By the present vention this activity is reduced by a process w ch is partly physical and partly chemical. By simple deposition or chemical decomposition on th carbon black surface, these inactivators reduce or destroy the adsorptive aflinity of this surface for drier compounds and so alter the chemical nature of this surface that its deleterious eflect on drying is either reduced or completely eliminated' It is, therefore, important that for a compound to be classed as an inactivator it should react favorably, both physically andchemically, with the carbon black. The drying retardation of carbon black is a conjoint action and must be dealt with accordingly, with due regard for both chemical and physical action of the carbon black so far as it affects its adsorptive power.

It seems reasonable to suppose that carbon black has a preferential afilnity for the inactivator or its reaction products over the oil soluble driercompounds, added or natural. And that this action is a selective one is indicated by the fact that there is considerable variation between the efiectiveness of the various inactivators, and

also by the fact. that some compounds, and certain compounds of the drier metals that might be expected to give beneficial results, are inoperative. Thus, calcium acid phosphate, and zinc sulphate actually retard the drying of coating compositions containing carbon black as. a pigc rbon black, there is evidence to believe that the salt undergoes some decomposition. This decomposition probably deposits an insoluble residue on the carbon black surface which reduces improved drying characteristics in carbon black pigmented coating compositions, first, must be of the type for which carbon black has a pronounced afllnity, and second, must either decompose or be fixed upon the surface of the car-' bon black in such manner as to prevent their dislodgment when the carbon black is ground into the liquid vehicle.

While the particular coating composition selected as an example in the foregoing description is an enamel, it is to be expected, and experiment has confirmed the fact, that the inactivators are equally efiicacious for other classes of liquid coating compositions, such as paints, inks, etc., in which oil or a resin, or a, combination of both, forms the vehicle for the carbon black pigment and drier metals.

Coating compositions produced from treated carbon black as described above in many cases are superior in physical characteristics-gloss,

depth of color, stability and'durabilit'yto coatcarbon black ing compositions in which untreated is used as the pigmenting agent.

activating compound comprising an inorganic salt of chromic acid, and then removing excess moisture from the carbon black by drying.

2. The method of treating carbon black for use as a pigment in, coating compositions included within the class consisting of drying oils and resins and containing a drier compound, which comprises applying to the carbon black an aqueous vehicle carrying an inactivating compound for rendering thecarbon black less reactive with respective to the drier compound, said inactivatingcompound comprising. an inorganic salt of chromic acid and in proportion not substantially exceeding one-tenth byweight of the carbon black, and then removing excess moisture from the carbon black by drying.

3. The method of treating carbon black for use as a pigment in coating compositions included within the class consisting of drying oils and resins and containing a drier compound, which comprises applying to the carbon black an aqueous vehicle carrying an inactivating compound for rendering the carbon black less reactive with respect to the drier compound, said inactivating compound being selected from the group of chromates and dichromates of the class consisting of copper dichromate, zinc' dichromate, manganese chromate, calcium chromate, cadmium chromate, chromium dichromate, colbalt We are aware of the patents of William B.

Wiegand, Nos. 2,178,382 and 2,178,383, both granted October 31, 1939, relating to the treatment of carbon black and lamp black with a compound designed to modify the pH of these blacks and thereby increase their dispersion properties.

We are also aware that it has been heretofore proposed to make an anti-rust coating composition consisting of the usual drying and binding agents together with a pigment obtained by saturating adsorbent pulverulent substancessuch as soot-with concentrated aqueoussolu tions of chromic acid or chromates followed by drying and grinding. This grinding is necessary presumably from the fact that whenthe mixture is dried the particles lump together and require grinding to break them down to sufilcient fineness so that they may serve effectively asa pigment. Our method of applying the chromates and dichromates in amounts adequate only for surface treatment of the carbon particles does not result in a product requiring subsequent dry guiding.

Furthermore we have found that high proportions of treating material decrease the coloring value of the carbon black being treated. By

our process, using limited amounts of chromates or dichromates, the coloring value may be enhanced.

The present invention is not to be restricted to any specific proportions or manner of procedure beyond the limitation of the appended claims. a

We claim:

1. The method of treating carbon black for use as a pigment in coating compositions included within the class consisting of drying oils and resins and containing a drier compound, which comprises applying to the carbon black an aqueous vehicle carrying an inactivating com- 7 pound for rendering the carbon black less. reactive with respect to the drier compound, said indichromate, magnesium chromate, strontium chromate, nickel dichromate, sodium dichromate, ammonium dichromate, potassium chromate, potassium dichromate, ferric dichromate and lead chromate, and then removing excess moisture from the carbon black by drying.

4. The method of treating carbon black for use as a pigment in coating compositions included within the class consisting or drying oils and resins and containing a drier compound, which method comprises applying to the carbon black potassium dichromate, and then removing excess moisture from the carbon black by drying.

5. The method of treating carbon black for use as a pigment in coating compositions included within the class consistsing of drying oils and resins and containing a drier compound,

which method comprises applying to the carbon black copper dichromate, and then removing excess moisture from the carbon black by drying. 6. The method of treating carbon black for use as a pigment in coating compositions included within the class consisting of drying oils and resins and containing a drier compound, which method comprises applying to the carbon black ferric dichromate, and then removing excess moisture from the carbon black by drying.

7. A carbon black pigment for coating coinpositions included within the class consisting of drying oils and resins and containing a drier compound, said carbon black having a surface film of an inactivating compound for rendering the carbon black less reactive with respect to thedrier compound, said inactivating compound "comprising an inorganic salt of chromic acid.

8. A carbon black pigment for coating compositions included within the class consisting of drying oils and resins and containing a drier compound, said carbon black having a surface film of an inactivating compound for rendering the carbon black less reactive with respect to the drier compound, said inactivating compound comprising an inorganic salt of chromic acid in proportion not substantially exceeding one-tenth by weight of the carbon black.

9. A carbon black pigment for coating compositions included within the class consisting of drying oils and resins and containing a drier compound, said carbon black having a surface film of an inactivating compound for rendering the carbon black less reactive with respect to the drier compound, said inactivating compound being selected from the group of chromates and dichromates of the class consisting of copper dichromate, zinc dichromate, manganese chromate, calcium chromate, cadmium chromate, chromium dichromate, cobalt dichromate, magnesium chromate, strontium chromate, nickel dichromate, sodium dichromate, ammonium dichromate, potassium chromate, potassium dichromate, ferric dichromate and lead chromate.

10. A carbon black pigment for coating compositions included within the class consisting of drying oils and resins and containing a drier.

compound, said carbon black'having a surface film of potassium dichromate.

11. A carbon black pigment for coating compositions included within the class consisting of drying oils and resins and containing a drier compound, said carbon black having a surface film of copper dichromate.

12. A carbon black pigment for coating compositions included within the class consisting of drying oils and resins and containing a drier compound, said carbon black having a surface film of ferric dichromate.

13. A liquid coating composition of the oxidizing-polymerizing organic vehicle type containing carbon black as a pigmenting agent and a drier compound, the carbon black having a surface film of an inactivatingcompound for rendering the carbon black less reactive with respect to said drier compound, said inactivating compound comprising an inorganic salt of chromic acid.

14. A liquid coating composition of the oxidiz-' ing-polymerizing organic vehicle type containing carbon black as a pigmenting agent and a drier compound, the carbon black having a surface film of an inactivating compound for rendering the carbon black less reactive with respect to said drier compound, said inactivating compound comprising an inorganic salt of chromic acid in proportion not substantially exceeding one-tenth by weight of the carbon black.

15. A liquid coating composition of the oxidizing-polymerizing organic vehicle type containing ing-polymerizing organic vehicle type containing carbon black as a pigmenting agent and a drier compound, the'carbon black having a surface film of potassium dichromate.

17. A liquid coating composition of the oxidizing-polymerizing organic vehicle type containing carbon black as a pigmenting agent and a drier compound, the carbon black having a surface film of copper dichromate.

18. A liquid coating composition of the oxidizing-polymerizing organic vehicle type containing carbon black as a pigmenting agent and a drier compound, the carbon black having a surface film of ferric dichromate.

MAX R. VOGEL. JOHN W. SNYDER. 

